1. Field of the Invention
The present invention relates generally to particulate matter filtration system and, more particularly, to a manhole filter apparatus for use in preventing the escape of dust from hopper containers and railcars during loading and unloading thereof.
2. Discussion of the Prior Art
A known system for transporting particulate matter employs a hopper trailer having a plurality of hopper spaces therein which are connected together internally to define a single storage container. At the lower end of each of the hopper spaces, a discharge chute is provided through which the particulate matter is delivered during unloading of the trailer.
Typically, in addition to the lower discharge chutes, a material inlet is provided on the trailer at or near the top of the trailer along with manholes to permit entry into the storage compartment.
Hopper trailers of this type may be loaded and unloaded in several different ways. For example, in accordance with one loading technique, particulate material is forced into the material inlet of the trailer under positive pressure exerted on the material at the feeding end of the transfer system. As the material enters the storage compartment of the trailer, pressure is relieved through the open manhole to the atmosphere. However, in order to prevent dust and fine particulate matter from escaping from the system into the environment, a filter apparatus is conventionally provided to remove the dust from the air exiting the compartment.
One known filter arrangement used in this type of loading operation includes a bag or sock filter having one open end that may be attached to the manhole in order to ensure that air exiting the manhole passes through the filter. However, there are several drawbacks to using this type of filter apparatus. For example, the sock filter is assembled on the manhole when the manhole is to be vented, and must be removed therefrom whenever the sock is cleaned. In addition, because of the construction of the sock filter, it fills with pressurized air during a loading operation and expands such that the sock extends upward from the manhole into the air above the trailer thus pulling on the sock filter with a force that is sufficient to pull the sock filter from the manhole upon clogging of the filter. When the filter comes loose from the manhole under such conditions, the sock filter and a significant amount of the pressurized dust-filled air blows through the manhole into the environment with significant force.
According to a second loading technique, a blower is connected to the manhole of the hopper trailer in order to create a vacuum within the compartment which draws material into the compartment through the material inlet from a material storage location such as a vented railcar or the like. When a loading operation of this type is carried out, the manhole is typically sealed such that a sock filter may not be employed.
In order to filter the air exiting the compartment upstream of the blower in the second loading method several methods exist. For example it is conventional to employ a cyclone filter which may either be mounted on the rear of the trailer or provided as a separate unit. In conjunction with the cyclone filter, it is known to provide an air filter through which the air passes after exiting the cyclone filter but prior to entering the blower. Of the known filters used in this construction, including paper, plastic tubes or felt materials, all require manual cleaning operations to be carried out periodically. It is also known to use tube filter arrangements as the only filter in environments separate from the environment of the present invention such as in silos and bins.
In review of the known loading arrangements it can be seen that no single filter arrangement is presently known which is versatile enough to find utility in both of the two noted loading methods while providing adequate filtration to protect blower machinery to meet with constantly increasing restrictions on the air quality of air being exhausted from transfer systems of the noted type.